Each year 1 in 100 children are born with a congenital heart defect, representing 40,000 children each year in the United States and 1,300,000 children worldwide with clinically significant congenital heart disease (“CHD”). Twenty five percent (25%) of pediatric CHD patients require invasive treatment to correct or palliate these defects and therefore undergo complex biventricular and univentricular repairs. These repairs involve cardiopulmonary bypass (“CPB”) procedures during surgery, as well as circulatory support in the pre or post operative periods. A prolonged CPB can potentially lead to neurological complications and developmental defects in up to 50% of these young patients i.e. infants and children from 2 to 25 kg with congenital or acquired cardiovascular disease.
During CPB, tiny arterial cannulae (2-3 mm inner diameter), with micro-scale blood-wetting features transport relatively large blood volumes (0.3 to 1.0 L/min) resulting in high blood flow velocities. These severe flow conditions are likely to result in platelet activation, release of pro-inflammatory cytokines, and further result in vascular and blood damage. The cannulae are required to provide high blood volume flow rates during neonatal and pediatric cardiopulmonary bypass procedures, resulting in high velocity jet flows. These severe flow conditions initiate platelet activation, release inflammatory cytokines, and further result in vascular and blood damage. Through the design of internal flow control features and a modified cannula outflow tip, it has been made possible to result in outflow jets with low exit force at high flow rates produced with low driving pressure drops, having minimal jet wake blood damage.
Recent investigations have indicated the high hemolytic risk of standard cannulae used in the setting of neonatal CPB surgery and post intervention recovery has been reported to remain suboptimal. Common arterial cannulation sites are located at the aorta, femoral, axillary or subclavian (with or without a side graft), external iliac, and innominate artery. Arterial perfusion by cannulation of the ascending aorta is regarded as an important advance in cardiovascular surgery and is the focus of the present invention since the technique eliminates the issues of retrograde aortic perfusion and the need for a second incision for femoral cannulation during CPB. The aortic cannula must ideally be placed high up in the ascending aorta (as discussed in R. Garcia-Rinaldi, et al., “Simplified aortic cannulation,” Ann Thorac Surg, vol. 36, pp. 226-7, August 1983) but improper technique can occasionally result in profuse bleeding as a result of improper cannula placement. To date, CPB has been studied in regard to clinical stroke-risk (see D. B. Andropoulos, et al., “Neuroprotection in Pediatric Cardiac Surgery: What is On the Horizon?,” Prog Pediatr Cardiol, vol. 29, pp. 113-122, Aug. 1, 2010), but there have been few reported studies deriving cannula design and device use strategy from fluid dynamics associated with arterial cannulation (see T. A. Kaufmann, et al., “Flow distribution during cardiopulmonary bypass in dependency on the outflow cannula positioning,” Artif Organs, vol. 33, pp. 988-92, November 2009; T. A. Kaufmann, et al., “The impact of aortic/subclavian outflow cannulation for cardiopulmonary bypass and cardiac support: a computational fluid dynamics study,” Artif Organs, vol. 33, pp. 727-32, September 2009; Y. Tokuda, et al., “Three-dimensional numerical simulation of blood flow in the aortic arch during cardiopulmonary bypass,” Eur J Cardiothoracic Surg, vol. 33, pp. 164-7, February 2008; A. F. Osorio, et al., “Computational fluid dynamics analysis of surgical adjustment of left ventricular assist device implantation to minimise stroke risk,” Comput Methods Biomech Biomed Engin, vol. 21, p. 21, Dec. 21, 2011), all underscoring the association of biomechanical risks with aortic cannulation. Despite these risks, outflow cannula design and cannulation methods have received little attention compared to the effort expended to assure the safety and efficacy of the mechanical circulatory support blood pumps. There is a definitive need for engineering small yet hemodynamically efficient arterial outflow cannulae that can provide high blood volume flow rates but with low exit force and outflow velocity, for use in extracorporeal circulation during neonatal CPB procedures, while minimizing recognized biomechanical risks related to infection, bleeding, hemolysis and thromboembolism during mechanical circulatory support.
Unlike adult CPB perfusion cannulae (U.S. Pat. No. 5,354,288 to Cosgrove, and U.S. Pat. No. 6,387,087 to Grooters, for example) where outflow is designed to have low velocity jets that prevent dislodgement of atherosclerotic plaque with adherent blood thrombi that can potentially cause thromboembolism, the design goal for the neonatal and pediatric population is quite different. In order to assess desirable jet wake hemodynamics in small cannulae, the jet's potential core length, resistance to outflow, and normalized index of hemoylsis as major parameters to designs so as to provide high blood volume flow rates but with low exit force and outflow velocity from far smaller cannula inner diameters that those used in adults—the latter being a requirement for minimizing disruption of the child's artery during cannulation. The focus of cannula design today and the goal of this invention are therefore to minimize risk of vascular injury and risks of biomechanical origin as well as to simultaneously improve outflow rate versus driving pressure drop perfusion characteristics, which become increasingly unfavorable at reduced outflow diameters, in the case of conventional end-hole type standard cannula configurations evidenced by the prior art. In the case of the specific application aortic cannulation, the present invention may additionally improve perfusion to the head-neck vessels of the aortic arch and therefore improve cerebral perfusion, mitigating neurological complications commonly reported (neurological morbidity is as high as 30% in infants and children) in conjunction with CPB in young patients. See Fallon, et al., “Incidence of neurological complications of surgery for congenital heart disease,” Arch Dis Child, vol. 72, pp. 418-22, May 1995 and H. L. Pua and B. Bissonnette, “Cerebral physiology in paediatric cardiopulmonary bypass,” Can J Anaesth, vol. 45, pp. 960-78, October 1998.